Among the extraordinary passions for eating uncommon things must be reckoned that which some peoples exhibit for eating earth or clay. Of this practice, which would appear to have once prevailed all over the world, numerous examples were cited by Captain J. G. Bourke, U. S. A., inf the Ninth Annual Report of the Bureau of Ethnology. In some places, the custom has degenerated into a ceremonial, while in others the eating of this strange food still prevails as a kind of necessity to the lives of those who are addicted to it. The Mexican devotees picked up a piece of clay in the temple of Tezcatlipoca and ate it with the greatest reverence, and also ate a piece of earth in swearing by the sun and earth. But the use of clay by the Mexicans was not merely a matter of ceremony, for the substance seems to have been an esculent in common use. Edible earth was sold openly in the markets of Mexico, and appears in the list of foods given by Gomara. Cabeza de Vaca says that the Indians of Florida ate clay, and that the natives offered him many mesquite beans, which they ate mixed with earth.
Venegas asserts that the Indians of California ate earth. The traditions of the Indians of San Juan Capistrano and vicinity show that they had fed up a kind of clay, which they often used upon their heads by way of ornament. The Tatu Indians of California, according to Powers, mix red earth into their acorn bread to make the latter sweet and cause it to go further. Sir John Franklin relates that the banks of the Mackenzie River contain layers of a kind of unctuous mud, which the Tinneh Indians use as a food during the seasons of famine, and even at other times chew as an amusement. It has a milky taste and the flavor is not disagreeable. The Apache and Navajo branches of the Athabascan family of North American Indians are not unacquainted with the use of clay as a comestible, although among the former it is now rarely used, and among the latter is employed only as a condiment to relieve the bitterness of the taste of the wild potato. In the same manner it is known to both the Zuni and the Tusayan. In South America, likewise, the eating of clay prevails among the Indians on the banks of the Orinoco, throughout Brazil, and on the mountains of Bolivia and Peru. In Western Africa, the negroes of Guinea have long been known to eat a yellowish earth called by them "caouac," and the flavor and taste of which is very agreeable to them and said to cause them no inconvenience. Some addict themselves so excessively to the use of it that it becomes to them a real necessity, and no punishment is sufficient to restrain them from the practice of consuming it. When the Guinea negroes were in former times carried as slaves to the West India islands, they were observed to continue the custom of eating clay.
But the "caouac" of the American islands, or the substance which the poor negroes attempted to substitute in their new homes for the African earth, was found to injure the health of the slaves who ate it, and so the practice was long ago forbidden and has possibly now died out in the West India colonies. In Martinique, a species of red earth or yellowish tufa was formerly secretly sold in the markets, but the use of it has probably ceased in the French colonies also. In Eastern Asia a similar practice prevails in various places. In the island of Java, between Sourabaya and Samarang, Labillardiere saw small square reddish cakes of earth sold in the villages for the purpose of being eaten. These were found by Ehrenberg to consist for the most part of the remains of microscopic animals and plants which had lived and been deposited in fresh water. Some of the Japanese, too, are addicted to the practice of eating earth. Dr. Love, some time ago, published an analysis of a clay which is eaten to a considerable extent by the Ainos; it occurs in a bed several feet thick in the valley of Tsietonai (eat-earth valley) on the north coast of Yesso. It is light gray in color and of fine structure. The people mix with the clay fragments of the leaf of some plant for the aromatic principle it contains. They eat the earth because they think it contains some beneficial substance, not because it is a necessity with them. They have meat and abundance of vegetable food. The clay is eaten in the form of a soup. Several pounds are boiled with lily roots in a small quantity of water, and afterward strained. The Ainos pronounce the soup very palatable. In Runjut Valley, in the Sikkim Himalayas, a red clay occurs, which the natives chew, especially as a cure for the goitre. In Smyth's Aborigines of Victoria, it is stated that a kind of earth, pounded and mixed with the root of the "mene" (a species of Haemadorum), is eaten by the natives of West Australia. In Northern Europe, especially in the remote northern parts of Sweden, a kind of earth known by the name of "bread meal" is yearly consumed by hundreds of cart loads, it is said. A similar earth is commonly mixed with bread in Finland. In both these cases, the earth employed consists for the most part of the empty shells of minute infusoria in which there cannot exist any ordinary nourishment. Some of the Siberian tribes when they travel carry a small bag of their native earth, the taste of which they suppose will preserve them from all the evils of a foreign sky. We are told that the Tunguses of Siberia eat a clay called "rock marrow," which they use mixed with marrow. Near the Ural Mountains, powdered gypsum, commonly called "rock meal," is sometimes mixed with bread. The Jukabiri of Northeastern Siberia have an earth of a sweetish and rather astringent taste, to which they ascribe a variety of sanatory properties when eaten. In North Germany, on various occasions where famine or necessity has urged it (as in long protracted sieges of fortified places) a substance called "mountain meal," similar to that used in Sweden and Finland, has been employed as a means of staying hunger. According to Pliny, the Romans had a dish called "alica" or "frumenta," made of the grain zea mixed with chalk from the hills of Puleoli, near Naples. According to the myths of the Cingalese, their Brahmins once fed upon earth for the space of 60,000 years.
Scientific American - March 23, 1895; page 186; Clay Eating